1. Field of Invention
The present invention relates to an internal combustion engine control apparatus and, more particularly, to an apparatus and a method for controlling an internal combustion engine installed in a hybrid-type vehicle that runs by selectively using two types of motors, that is, an internal combustion engine and, for example, an electric motor.
2. Description of Related Art
For environmental protection, there is a demand for a maximum-possible reduction of emissions from an internal combustion engine installed in a motor vehicle. To meet such a requirement, one type of motor vehicle that stops its internal combustion engine in accordance with the running condition of the vehicle has been proposed. As an example of this type of motor vehicle, a hybrid motor vehicle is disclosed in Japanese Patent Application Laid-Open No. HEI 6-48190. This hybrid motor vehicle is equipped with two types of driving motors, that is, an internal combustion engine and an electric motor, and switches between them in accordance with the running condition of the vehicle. More specifically, during high-speed running, the internal combustion engine is operated in order to output high power which is required. When the running speed of the vehicle is low and the depression of the accelerator pedal is small, the electric motor is used to drive the vehicle since high power is not required in such a running condition The internal combustion engine is stopped while the electric motor is used to drive the vehicle, thereby significantly reducing emissions from the internal combustion engine in comparison with ordinary internal combustion engine-driven vehicles.
In a typical internal combustion engine, operation control is performed in various manners so as to maintain a good operating condition of the engine. In order to achieve an operating condition of the internal combustion engine as good as the present condition compared to when the next operation control is started, a control value is used for the present operation control and is stored as a learned value. That is, a control value for the operation control of the internal combustion engine is learned, and the learned control value is used the next time the operation control is started, so as to achieve as good an operating condition of the internal combustion engine at the start of the next operation control.
In the hybrid motor vehicle as described above, however, since the internal combustion engine is not always in operation, the opportunity of learning the control value for the operation control of the engine is correspondingly reduced. Reduction in the opportunity of learning the control value may lead to degradation of the appropriateness of the control value stored as a learned value. If this happens, the operation control based on the learned control value will fail to achieve as good an operating condition of the internal combustion engine.
While the hybrid motor vehicle is stopped, the idling of the internal combustion engine is performed only when there is a load, for example, a load for charging the battery, and the idling operation is not performed when there is no load. Therefore, unlike ordinary motor vehicles, the hybrid motor vehicle does not perform idle speed control in which during non-load idling, a throttle valve opening (flow of intake air) is adjusted so that the actual idle speed approaches a target revolution speed. Therefore, in the hybrid motor vehicle, the throttle valve is not controlled at an opening under the non-load condition, and the throttle valve opening under the non-load condition (defined as "closed state") is not maintained.
Since the hybrid motor vehicle is unable to perform learning control of the throttle valve opening when the throttle valve is in the closed state, the closed-state opening of the throttle valve, that is, the opening of the throttle valve in the closed state defined above, must be set to a fixed value. Therefore, in the hybrid motor vehicle, the closed-state opening of the throttle valve may be excessively closed or excessively opened relative to the proper opening of the throttle valve as the proper opening varies in accordance with the operating condition of the internal combustion engine. If, for example, the internal combustion engine is idling to charge the battery when the closed-state opening of the throttle valve is significantly smaller than the proper opening, the revolution speed of the engine may become lower than a proper value so that the battery cannot be sufficiently charged. If the closed-state opening of the throttle valve is significantly greater than the proper opening, the revolution speed of the internal combustion engine may become higher than the proper value, thereby leading to deterioration of the drivability.